All issues / Volume 15 (2021) / Issue 6 (June)
No abstarct. This is editorial corner.
Entanglement dynamics of uniaxially-oriented, disentangled ultra-high molecular weight polyethylene nanocomposites modified with gold nanoparticles are investigated, using dielectric spectroscopy, during the transition to melt state. The dc conduction is approximately calculated via the logarithmic derivative of dielectric permittivity and is observed to decrease with the formation of entanglements. As the draw ratio increases, the progressive formation of entanglements resulted in a stronger dc conductivity decrease due to the loss of orientation in the pre-melt crystalline and partially oriented amorphous chain segments. Additionally, a sharp peak is obtained in the absence of dc conductivity, attributed to the dipolar contribution of the Maxwell-Wagner-Sillars (MWS) interfacial polarization between the gold nanoparticles and the polymer chains. The relaxation time of the MWS interfacial polarization increases with the progressive formation of entanglements, as observed in a previous study. The results presented shed light on the process of entanglement formation in oriented ultrahigh molecular weight polyethylene nanocomposites.
The development of carbon fabric reinforced epoxy (CF/EP) composites with excellent mechanical properties and high flame retardancy is desired in both scientific and industrial communities. In this work, the phosphorus-containing flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) based amine functional silane coupling agent was coated on carbon fabric, aiming to promote the interfacial charring behavior, and at the same time, improve the fiber-matrix interfacial strength. With only a small proportion of the hybrid Si/N/P coating on the fiber surface, the resultant composite laminate showed a 26 and 31% reduction in peak heat release rate and smoke production rate, respectively. Under the combustion, the surface grafted phosphorus compounds effectively promoted the interfacial charring behavior of EP composites. An integrated and dense char layer composed of carbon fabric with sealed gaps was formed to protect the underlying polymer materials in the condensed phase. In addition, the fiber push-in test clearly revealed an increased fibermatrix interfacial strength (35%) due to the existence of amine groups on the fiber surface. The provided Si/N/P hybrid surface functionalization strategy proved to be an effective approach to prepare high-performance flame retardant CF/EP composite.
The study presents new on/off switchable nanofiber membranes with high sensitivity for detecting Co2+ and Cu2+ ions. The nanofiber membranes were fabricated by electrospinning (ES) the poly[(2-hydroxyethylmethacrylate-co-N-methylolacrylamide)] [poly(HEMA-co-NMA)] copolymer with different quantities of 2,2′-bipyridine-3,3′-diol (BPDO). Poly(HEMA-co-NMA)random copolymers with various molar ratios of the HEMA and NMA monomers were synthesized by free radical polymerization. The HEMA and NMA moieties were specifically selected to promote hydrophilicity and crosslinking reactions, which ultimately support a mechanically stable structure in aqueous media. ES nanofiber membranes S1-0.5, with a HEMA:NMA molar ratio of 77:23 and 0.5 wt% of BPDO showed strong photoluminescence quenching upon exposure to Co2+ and Cu2+ ions at concentrations ranging from 10–7 to 10–4 M. Moreover, the nanofiber membranes exhibited reversibile on/off fluorescence emission properties upon the sequential addition of Cu2+ ions and ethylenediaminetetraacetic acid (EDTA). These results demonstrate a simple fabrication strategy for nanofiber membranes that have the potential to be effective for the real-time sensing of metal ions.
Self-confined synthesis of silver nanoparticles (AgNPs) within mesoporous host matrixes based on poly(ethylene terephthalate) (PET) upon X-ray radiolysis is studied. Mesostructured PET matrixes with a porosity of 35 vol% and pore dimensions below 10 nm were prepared and loaded with Ag+ ions via the mechanism of environmental crazing. Upon subsequent X-ray irradiation of silver-loaded samples, Ag+ ions experience reduction into Ag0 within mesopores. In this case, solvated electrons, alcohol radicals, and acetaldehyde act as effective reducing agents. The calculations show that the X-ray absorption dose rate for the solutions of silver nitrate (33.6 Gy/s) is nearly three times higher than that of pure PET (10.1 Gy/s). This contrast allows a selective synthesis of AgNPs within mesopores whereas the dose rate for the PET matrix lies within the level of sterilization. Mesoporous matrixes provide confined conditions for the synthesis of AgNPs with mean dimensions of ~2–3 nm and also serve as a stabilizing medium that prevents their aggregation and spares the use of any capping agents. This reagent-free approach offers a new route for preparing diverse hybrid organo-inorganic nanomaterials with desired functional properties.
Graphene nano-platelets (GNPs) can substantially improve the performance of epoxy resin, but improving effects are highly dependent on GNP dispersion uniformity in the matrix. The aim of the current study is to explore the influence of matrix viscosity on the dispersion of GNPs. Thus, epoxy matrix with three disparate viscosities was reinforced with GNPs varying from 0 to 3 wt%, and the influence of matrix viscosity on dispersion uniformity and thus properties of composites were identified. Significant differences in rheological and electrical percolation thresholds were found with a change in the matrix viscosity. The lowest rheological percolation threshold (0.3 vol%) and electrical percolation threshold (0.53 vol%) were always observed in specimens based on a low viscosity matrix. X-ray Diffraction (XRD) results also showed that lower viscosity resulted in better GNPs distribution. The visual state of GNPs dispersion with a change in matrix viscosity was also evaluated through Scanning Electron Microscopy (SEM) and optical microscopy. Optical microscopy images confirmed that while the GNP agglomeration diameter is 42.3 µm in high-viscosity resin, it markedly decreased to 15.1 µm by using low viscosity resin. Transmission Electron Microscopy (TEM) quantitative measurements pertaining to the number of GNP stacked layers also showed that when a low viscosity matrix was used, only 11 layers stack on each other and form thinner clusters compared to 13 and 39 layers in medium and high ones.
Hybrid microspheres and percolated monoliths synthesized via Pickering emulsion co-polymerization stabilized by in situ surface-modified silica nanoparticles
B. Fouconnier, F. Lopez-Serrano, R. I. Puente Lee, J. E. Terrazas-Rodriguez, A. Roman-Guerrero, M. C. Barrera, J. Escobar
Vol. 15., No.6., Pages 554-567, 2021
Vol. 15., No.6., Pages 554-567, 2021
The Pickering emulsion polymerization of styrene (St), divinylbenzene (DVB) as a crosslinking agent, and sodium 4-vinyl benzene sulfonate (VBS) used for in situ surface-modification of silica nanoparticles (SNps) was investigated. At 1.0 wt% DVB, amphiphilic SNps with hydrophobic patches were formed, further self-assembling into copolymer-SNps clusters occurred. Subsequently, these clusters grow by monomer swelling to finally lead to the formation of core-shell polymer microspheres. Unlike the hydrophilic patchy SNps, at 2.0 and 3.0 wt% DVB, surface-patterned SNps with higher effective hydrophobicity do not self-assemble in the water phase but rather lead to the formation of monoliths. The polymerization mechanisms related to the formation of polymer silica-coated microspheres hybrid-materials, or percolated monoliths with bi-continuous porosity, formed by interfacially jammed emulsion gel (bijels) templates, are discussed herein.
Patients sometimes lose organs and/or organ functions due to disease and injury, which may result in permanent disabilities. Advanced biotechnological practices can now afford victims of these incidences an opportunity to repair some of the damaged tissues or organs without the need for a donor. This can be achieved by reconstruction of the damaged tissue or organ through scaffold and cell technologies. Scaffolds serve as template material for neo-organs to guide and accelerate cell growth. The structure of a scaffold material must meet certain design parameters to achieve optimal functionality in tissue engineering. Pre-requisites include surface compatibility and architectural suitability with the host environment. Polymeric scaffolds derived from polymer blends have the prospects to control the physical and chemical environment of the biological system. In this review, potential roles, general properties, advantages, and disadvantages of poly (lactic acid) and its composites as functional materials for scaffolding will be outlined. PLA and its composites have been subjects of research for some decades due to non-toxicity and the ability to mimic native tissue. Though PLA and composites have demonstrated great potential for various biomedical applications, a lot still needs to be done for them to compete with donor and prosthetic organs.